1. Field of the Invention
The present invention relates to testing a thin-film magnetic heads with a magnetoresistive effect (MR) elements and in particular to testing multiple MR elements that are placed under long term thermal stress.
2. Discussion of the Related Art
It is desirable to test the lifecycle of magnetoresistive (MR) elements to ensure long term adequate performance. Generally, testing the lifecycle of MR elements includes stressing MR elements with an increased ambient temperature while applying bias current to the MR element and/or write element.
In one type of conventional lifecycle testing, the MR elements are stressed and tested in an environment with a raised ambient temperature, i.e., in an oven. Typically, in an oven tests, a number of MR elements are connected to a bias current source, the MR elements are heated and the resistance in the MR elements is tested.
Resistance measurements of MR elements, however, is a relatively crude assessment of the MR elements performance. In general, a more thorough analysis of the performance of the MR elements is desirable. By way of example, MR elements can be more thoroughly analyzed using Quasistatic tests such as, Amplitude, Asymmetry, Barkhausen Jump, Spectral Maximum Amplitude Noise (SMAN), and Popcorn Noise, which are well known in the art. Quasistatic tests are performed within a magnetic field, and typically require a short cable connection, e.g., 2 to 3 inches, to the MR element. Oven tests, on the other hand, do not include magnetic fields and use relatively large connections, e.g., 2 feet.
Another conventional lifecycle test is performed at the head gimbal assembly (HGA) level, i.e., where the MR head is mounted on the HGA and can include Quasistatic testing. Testing at the HGA level is advantageous because it can be done within the magnetic fields and uses short cable connections. During testing, the MR heads are placed on a heating block and the bias and writing stresses can be applied through the HGA. Typically, HGA lifecycle testing is performed on 1 to 8 heads at a time. Current technology, however, limits the tests to a maximum of approximately 8 heads due to size constraints of magnetic fields and short cable connects. Thus, if a large data sample is desired, many testers are required. Further, HGA level tests are late in the manufacturing process, i.e., the processing of the MR heads must be completed and the heads mounted on the head gimbal assembly prior to testing.
Thus, what is needed is a lifecycle tester that can perform Quasistatic tests on many MR elements simultaneously early in the process.